The present invention relates to a method for embedding an embedded part such as a nut in a base made of thermoplastic resin.
Conventionally, in order to embed a metal nut for mounting a part such as a solenoid valve in a base made of thermoplastic resin, a hole smaller than an outer peripheral shape of the metal nut is first formed in the base, the metal nut is axially aligned with and disposed on the hole, and then a horn of an ultrasonic oscillator is brought into contact with the metal nut, ultrasonic vibration is applied to the metal nut through this horn to thereby generate frictional heat between the metal nut and the base. While melting and plasticating a periphery of the hole in the base by this frictional heat, the metal nut is pressurized and press-fitted in the hole by the horn.
However, because the above method for embedding the metal nut by using ultrasonic vibration requires equipment and devices such as the ultra sonic oscillator, the cost is high. Moreover, because rigidity of the base made of resin is low and a portion of the base in contact with the metal nut is softened by the frictional heat when the metal nut is press-fitted in the hole of the base by the horn, the metal nut is liable to be press-fitted in a tilted state and it is difficult to embed the metal nut with accuracy. Furthermore, it is difficult to embed the metal nut in an intermediate portion of a wall thickness of the base in a state in which a hole having a diameter smaller than an outside diameter of the metal nut is communicating with an entrance side of the intermediate portion.
The present invention has been accomplished with the above problems in view and it is an object of the invention to provide a method for embedding an embedded part in a base with accuracy.
It is another object of the invention to provide a method for embedding an embedded part in an intermediate portion of a wall thickness of a base in a state in which a hole having a diameter smaller than an outside diameter of the embedded part is communicating with an entrance side of the intermediate portion.
To achieve the above objects, according to the invention, there is provided a method for embedding a part, wherein an embedding hole is formed in a base made of thermoplastic resin, an embedded part is inserted in the embedding hole, the base is subjected to heating treatment for softening the base to bring the base into an elastomeric region and restraining treatment for restricting outward thermal expansion of the base to thereby expand the base in an inward direction of the embedding hole to reduce a hole diameter and to deform a hole wall of the embedding hole along a shape of an outer wall face of the embedded part and to bring the hole wall into close contact with the outer wall face, and then the base is cooled and hardened to thereby fix the embedded part in the embedding hole.
The base may be subjected to the heating treatment and the pressurizing treatment at different steps but the base is preferably heated while restricting outward thermal expansion of the base.
According to the method of the invention having the above structure, because the embedded part is inserted in the embedding hole of the base in advance and the base is heated in this state to thereby reduce the hole diameter of the embedding hole and to fix the embedded part in the embedding hole, it is possible to embed the embedded part straight in the embedding hole of the base with accuracy by a simple method as compared with a prior-art method in which the embedded parts are successively press-fitted in the base while softening the base by frictional heat due to ultrasonic vibration.
According to an embodiment of the invention, means for restricting the thermal expansion of the base is a metal mold and the base is heated while the base is housed in the metal mold.
According to another embodiment of the invention, both means for heating the base and means for restricting the thermal expansion are fluid and the base is immersed in the fluid and heated while being pressurized from a periphery by the fluid a temperature and pressure of which have been increased in a state in which the base is vacuum-packed in a covering having heat resistance, airtightness, and flexibility.
In the invention, by making a depth of the embedding hole formed in the base larger than a length of the embedded part and inserting the embedded part on a bottom portion side of the embedding hole, it is possible to form a small-diameter portion having a diameter smaller than an outside diameter of the embedded part on an entrance side of the embedding hole by reduction of the hole diameter.
As the embedded part, a nut having an outer surface provided with a depression and a projection is used suitably.
According to the invention, there is provided a method for embedding a part in a base made of thermoplastic resin, wherein a first base made of thermoplastic synthetic resin in which an embedding hole is formed in a junction face and an embedded part is inserted in the embedding hole and a second base made of thermoplastic synthetic resin having a through hole are joined to each other with the through hole communicating with the embedding hole, a joined body is subjected to heating treatment for softening both the bases to bring the bases into an elastomeric region and pressurizing treatment from a periphery to thereby expand both the bases in an inward direction of the embedding hole to reduce a hole diameter, to deform a hole wall along a shape of an outer wall face of the embedded part to bring the hole wall into close contact with the outer wall face, and to weld and integrate both the bases to and with each other through the junction faces, and then the joined body is cooled and hardened to thereby embed and fix the embedded part in an intermediate portion of the integrated two bases.
According to an embodiment of the invention, means for pressurizing the joined body is a metal mold and the joined body is heated and pressurized while the joined body is housed in the metal mold.
According to another embodiment of the invention, both means for heating the joined body and means for pressurizing the joined body are fluid and the joined body is immersed in the fluid and heated and pressurized by the fluid a temperature and pressure of which have been increased in a state in which the joined body is vacuum-packed in a covering having heat resistance, airtightness, and flexibility. It is also possible that the joined body is subjected to heating treatment by proper means and then immersed and pressurized in the fluid.